Analysis of Long-Distance Heavy Rainfall Caused by Typhoon Mangosteen (2018)

TRP (Tropical cyclone Remote Precipitation), usually a high-impact weather phenomenon, is difficult to forecast accurately. In this paper, ground and sounding observation data, radar remote sensing data, and NCEP re-analysis data at 0.5°×0.5° resolution and 6-h intervals were used to analyze the physical process of the long-distance rainstorm in the Yangtze River Delta region associated with typhoon Mangosteen during its landfall in Guangdong Province in 2018. The results show that: (1) The TRP event occurred under the control of the western North Pacific subtropical high, and was affected by typhoon’s inverted trough in the lower layer. (2) The heavy rain in the first stage was mainly caused by strong convective instability, which was triggered by a convergence line in the typhoon Mangosteen inverted trough in the lower troposphere. Mangosteen poloidal outflow at upper levels merged into the mid-latitude westerly wind over the Yangtze River Delta region, thus strengthening upper divergence and upward movement in the rainstorm area. In the second stage, convective instability was weakened, but a low pressure vortex had been formed at the north end of the typhoon’s inverted trough at 850 hPa and a short-wave trough developed subsequently at the edge of the subtropical high at 500 hPa, so that dynamic conditions for a rainstorm were more favorable. (3) The three heavy rainfall centers in the Yangtze River Delta region were located at the mouth of the Yangtze River, along the coast of Jiaxing on the north coast of Hangzhou Bay and along the coast of Ningbo, all of which were near the land-boundary. (4) The diagnosis of vorticity budgets on the remote rainstorm area suggest that the initial disturbance of the rainstorm was mainly forced by the horizontal convergence and divergence terms near the surface, and then a low pressure vortex at 850 hPa developed due to the horizontal convergence and divergences terms combined with the twisting term. These were related to the lower-level southerly jet between the inverted trough and the subtropical high. Finally, vorticity was increased upward to the mid-layers (700–500 hPa), attributed to vertical ascending motion, resulting in the development of a short-wave trough at 500 hPa at the edge of the subtropical high. (5) In the formation of the long-distance rainstorm, a lower layer southerly jet formed between typhoon Mangosteen and the western North Pacific subtropical high to transport water vapor to the Yangtze River Delta area, which was similar to a typical TRP event. The difference is that the initial disturbance in a typical TRP is generally provided by the westerly trough in mid-latitudes, while in this rainstorm, it was mainly provided by Mangosteen’s inverted trough and the low-level southerly jet. Vorticity was then transported upward, leading to the development of a short-wave trough.